Botany - B.E. Yakubenko 2017

Part Three. The Plant Kingdom (Plantae)
Chapter IX. Division Angiosperms, or Flowering Plants (Angiospermae, Magnoliophyta)
Laboratory Session Topic 14.39. Structure of the Anther, Ovary, and Ovule

General Remarks. The anther is the bearer of male hereditary information. In the anther locules, microspore tetrads are formed from sporogenous tissue As a result of Meiosis. They germinate into a pollen grain, which represents the male gametophyte of a flowering plant. As a sporogenic organ, the anther has a complex Structure. When examining it, pay attention to the structural features and Functions of its individual parts.

The Ovary also features complex Cytology/cytology/67.html">Development and Structure. Its locules contain ovules, in which megaspore tetrads are formed from an archesporial Cell via meiosis. One of them develops into the embryo sac (the female gametophyte).

During double Fertilization, an embryo develops from the diploid zygote resulting from the fusion of the egg cell and a sperm cell, while the endosperm is formed from the triploid zygote resulting from the fusion of the central cell and a sperm cell. Consequently, a seed develops from the ovule, and a fruit develops from the ovary.

Object. Subclass Liliidae, order Liliales, family Liliaceae, representative — Turk's cap lily (Lilium martagon L.)

Tasks:

1. Study and draw The structure of the anther.

2. Study the Structural Features of the ovary and ovule.

3. Study the STRUCTURE OF THE embryo sac.

4. Draw the observed objects in your workbook and label their constituent parts.

Equipment and Materials: MBR-1 or Biolam microscopes, live and herbarium material, models, scalpels, razor blades, magnifying glasses, prepared slides, charts, and other accessories.

Microscopic examination of the anther slide of Lilium martagon. Using low and high Microscope magnification, carefully examine and draw the structure of the anther. Note that the anther has a clearly defined single-layered epidermis, the outer walls of which are covered with a continuous cuticular film. Beneath the epidermis, a layer of Cells with spiral or reticulate Cell wall thickenings stands out; this is the fibrous layer. It plays a role in the dehiscence of the anther locules. From the inner side, they are lined with a tapetum (nutritive layer). The anther locules are filled with pollen grains. The central part of the anther is occupied by the connective parenchyma. A vascular bundle is located in its upper part (Fig. 105).

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Figure 105.

Microscopic examination of the ovary slide of Lilium martagon. It is advisable to examine the slide under low and high microscope magnification. You will easily recognize the single-layered epidermis with cuticle surrounding the inner Tissues of the ovary. Beneath it lies a multilayered, thin-walled parenchyma of the ovary walls. Find the slightly condensed, small-celled vascular bundles within it, and determine their number based on the curvature and junctions of the carpels. The innermost layer forms the lining layer bordering the ovary locules. In the center of the ovary is the Placenta, or central placenta, formed by parenchymatous tissue. Ovules are attached to the placenta by short stalks. An embryo sac is visible in each of them.

Figure 106. Structure of the ovule:

1 — micropyle; 2 — integuments;

3 — nucellus; 4 — synergid; 5 — egg cell; 6 — egg apparatus;

7 — central cell; 8 — antipodals;

9 — embryo sac; 10 — stalk (funiculus)

Microscopic examination of the ovule slide of the ovary. Using high microscope magnification, study the structure of the ovule. Two large multicellular layers, the integuments, or coats, are easily distinguished. At the apex, they do not fuse, forming the micropyle, or pollen chamber. Deeper lies the massive nucellus, within which the embryo sac is clearly discernible. At the micropylar end, three cells are visible that together form the egg apparatus: the middle one is the larger egg cell, and the two lateral ones are smaller synergids. In the center of the embryo sac lies its central cell with a secondary Nucleus. At the chalazal pole, three antipodal cells are located (Fig. 106).

Conclusion. The Analysis of the studied slides confirms that the gametophytes of angiosperms have undergone significant reduction in the course of evolution compared to other higher plants. The male gametophyte (pollen grain) develops in the anther locules, while the female gametophyte (embryo sac) develops in the megasporangia located within the ovule. The latter is formed in the ovary locules.

Self-control questions

1. In which part of the anther is the male gametophyte formed?

2. What represents the male gametophyte? What is microsporogenesis?

3. Explain The process of female gametophyte formation and its structure.

4. What is formed from the ovule and its individual parts?

5. What develops from the diploid and triploid zygotes?

6. Explain the Methods and sites of ovule attachment within the ovary.

7. Explain what polyembryony is and what types of it exist.

8. Explain what develops from the ovary and its individual parts.

11. Which PARTS OF THE ovule participate in seed formation?